Jackson . — Anatomical Structure of the Roots of Barley . 29 
shown in Fig. 8. In this case the central part of the stele is traversed by 
four large ducts separated from each other by thickened cells, but the 
actual boundary wall of each duct remains thin. Each xylem group 
contains one large vessel situated on the inner side of the protoxylem 
elements, and the groups are separated by small parenchymatous cells, 
among which the phloem cells are not easily distinguishable. The peri- 
cycle is composed of cells elongated radially and thickened uniformly on 
all the walls. Its continuity is interrupted opposite each of the xylem 
groups where the protoxylem elements abut directly on the endodermis. 
Here again passage cells occur, for the endodermis cells adjoining the 
piliferous lay er.. 
part of a TS of an 
Intermediate "an branched" root (x 46] 
Fig. 7. 
pari of a T:S: of an 
Old "unbranched’ rxntfx ’ 
Fig. 8. 
protoxylem elements are entirely unthickened, whereas thickening does 
occur on the radial walls of some of the other endodermis cells. Outside 
the endodermis are six to eight rows of large parenchymatous cortical cells, 
bounded by a well-marked piliferous layer. 
A longitudinal section of an ‘ unbranched ’ root shows that the ducts 
consist of wide elongated parenchymatous cells, the transverse septa being 
of the same thickness as the longitudinal walls. When two ducts appear 
in the section they are separated by several rows of cells, some of which 
have square, while others have pointed end-walls. The former are the 
thin-walled cells on the outer edge of the central stelar tissue, while the 
latter are the sclerized cells of the actual centre. The outer edge of 
the duct is bounded by a band of parenchymatous cells with square end- 
